Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
There is known a typical image forming apparatus, which forms an image on a sheet, that includes an apparatus main body, a photoreceptor drum (an image carrier), and a developing device. The developing device includes a developing roller opposed to the photoreceptor drum. There is provided a technique where a developing device is attachable/detachable with respect to an apparatus main body.
The developing device is attached to and detached from the apparatus main body as an image forming unit. The apparatus main body includes a rail member and a cutout portion formed at one end of the rail member. On the other hand, the image forming unit includes a roller that is rotatable and rotates on the rail member. In attaching the image forming unit, the roller derailing from the rail member and entering the cutout portion positions the image forming unit at a predetermined position inside the apparatus main body.